Control devices for braking mechanisms using energy-storing springs are already known. It is the task of the braking mechanisms using energy-storing springs, among others, to actuate the brake, upon failure of the electrical devices, i.e., upon current failure for any reason whatever without the supply of any external energy. A braking mechanism using an energy-storing spring of this type is described and illustrated in the brochure of the "RACO G.m.b.H. Schwelm," August 1970.
The construction of a braking mechanism using an energy-storing spring includes two basic structural parts -- the energy-storing spring and the electric drive therefor. The rotating motion of the motor is changed to a translatory motion of a spindle rod through a ball-type spindle with an associated nut disposed in the hollow shaft of the armature. The kinetic energy of the motor is thus transferred to the energy-storing spring. An electromagnetic brake is flange-mounted on the rear end of the braking device, which maintains the energy state of the stressed energy-storing spring with the least expenditure of energy upon the brake being released. The energy supply to the electromagnetic brake is interrupted via a magnetic contactor for braking of the vehicle. The energy-storing spring is then relaxed and is able to rotate the motor freely through the installed mechanism.
If the free stroke of the spindle has been covered, then the energy-storing spring has reached the force of the initial stress corresponding to the lowest braking force. The braking force is changed during the path of the stroke according to the spring characteristics of the energy-storing spring. The motor of the braking mechanism is switched "ON" through a second magnetic actuator for the release of the brake of the vehicle. The translatory motion of the spindle stresses the energy-storing spring, and towards the end of the stroke path, an installed switch switches the motor magnetic contactor "OFF," and switches the magnetic contactor of the electromagnetic brake "ON." The energy-storing spring is then again ready for braking.
In another brochure of the "RACO G.m.b.H. Schwelm," August 1972, another construction of the braking mechanism having an energy-storing spring is described and illustrated. The implementation described above has been expanded by a self-actuating and adjusting device and by a manually releasable device. This version is provided with a switch for braking stages, which contains resistors for the braking stages and is controlled dependent on weight or velocity. This control of the braking force by means of the resistors, does not, however, permit an unambiguous and reproducible relation with respect to the braking force, which is independent of any fluctuations of the control voltage and power supply, as well as of the direction of rotation. Additionally, the demand for electric energy is considerable in the intermediate stages.